The present invention relates generally to the area of fluid spraying and dispensing and more particularly to a nozzle construction for dispensing a spiral pattern of elongated strands of a heated hot melt adhesive onto a surface of a substrate.
Hot melt thermal plastic adhesives have been widely used in industry for adhering many types of products and are particularly useful in applications where quick setting time is advantageous. Further, bonding materials such as chopped fibers or fluff-type material forming a non-woven layer presents additional problems in dispensing the adhesive so that only the surface of the non-woven layer is bonded. Further, the adhesive must be sufficiently thinly applied so that its presence is not apparent on the opposite side of the substrate to which the non-woven material is being bonded such as a polyurethane sheet. In order to create elongated thin beads of adhesive, the dispensing nozzle has a plurality of air jets connected to a common air manifold which in turn is connected to a source of pressurized air. The air jets are arranged in the nozzle such that they tangentially contact the bead of adhesive as it is dispensed from the nozzle. The force of the air jets is effective to stretch and rotate the dispensed adhesive bead such that it is applied in a relatively compact spiral pattern on the substrate.
Depending on the application, it is also desirable to change the diameter of the adhesive bead being dispensed from the nozzle. Consequently, preferably the nozzles are exchangeable without requiring a different manifold, nozzle mounting plate or disassembly of the spray head. These problems are addressed by the nozzle disclosed in U.S. Pat. No. Re. 33,481 issued on Dec. 11, 1990 to R. A. Ziecker et al. which is assigned to the same assignee as this invention.
The nozzle disclosed in the '481 patent is adapted to mount to a threaded extension of a standard adhesive spray head, or spray gun. An adhesive discharge opening in the threaded extension is connected to an adhesive passage in the spray head body, and an air discharge opening in the threaded extension is connected to an air passageway in the spray head body. The nozzle has a spray disk which has a boss extending outwardly from a first, rear surface of the spray disk and a nozzle tip extending outwardly from a second, front surface of the spray disk. When the nozzle is mounted to the threaded extension, a through bore extending through the spray disk, boss and nozzle tip communicates with the adhesive discharge opening in the threaded extension of the spray head body. Heated hot melt adhesive is transmitted from the adhesive passage in the spray head body, through the adhesive discharge opening in the threaded extension and then into the through bore in the nozzle. The adhesive is ejected as an extruded bead through the nozzle tip toward a substrate.
The nozzle of the '481 patent is formed with an annular notch or groove which extends from its rear surface having the boss toward the front surface formed with the nozzle tip, and is located radially outwardly from the through bore in the nozzle. The annular groove is provided to assist in drilling bores in the spray disk through which jets of pressurized air are directed at an angle of about 30 degrees, and substantially tangent to, the adhesive bead ejected from the nozzle tip. While the nozzle disclosed in the '481 patent facilitates accurate drilling of the air jet bores and produces an acceptable spiral pattern of a strand or fiber of adhesive, some deficiencies have been discovered in certain applications. The nozzle is mounted to the threaded extension by a threaded mounting nut, and it has been found that the mounting nut can be over-torqued when the nozzle is installed. Such over-torquing of the mounting nut urges the periphery of the spray disk against the threaded extension of the spray head with such force that the spray disk can deflect or distort thus creating a leakage path at the interface between the nozzle boss and the threaded extension. In some instances, it has been found that hot melt adhesive has flowed radially outwardly along this leakage path into the annular groove where the pressurized air enters the air jet bores in the spray disk. This can clog the air jet bores and thus restrict the flow of air necessary to attenuate or stretch the adhesive bead to form an elongated adhesive fiber.
In addition to overtightening of the nozzle, another problem can occur during the assembly operation. Because the nozzle and mounting nut are separate pieces, the operator must properly orient the nozzle relative to the threaded extension of the spray head body before securing it with the mounting nut. Occasionally, the nozzle is installed upside down, i.e., with the nozzle tip facing the threaded extension and the boss facing outwardly, which ruins the nozzle tip and requires replacement of both the threaded extension and the nozzle.
Another potential problem with the nozzle disclosed in the '481 patent is that the front surface of the nozzle spray disk from which the nozzle tip extends is not mounted flush with the rim of the mounting nut which secures the nozzle to the threaded extension of the spray head body. As a result, a cavity or space is formed between the nozzle tip and the rim of the nut. Particularly when the dispenser is operated intermittently, it has been found that cut-off drool, i.e., adhesive remaining after the spray head is shut off, can collect in the space or cavity between the nozzle tip and the mounting nut. This cut-off drool can collect and clog the air jet bores formed in the nozzle, thus inhibiting the formation of an elongated adhesive fiber. In addition, a collection of adhesive fibers within such cavity is difficult to clean.
The potential problems with the nozzle disclosed in the '481 patent have been addressed in a one-piece nozzle cap manufactured and sold by Nordson Corporation of Amherst, Ohio, the assignee of this invention. The nozzle cap is formed from a section of hex-shaped bar stock such that the mounting nut and nozzle are integrally formed in a single, unitary construction instead of two separate pieces as in the '481 patent. A bore is drilled and tapped in the hex stock to form the mounting nut portion of the nozzle cap, and the nozzle is formed where such bore terminates. A first side, or rear surface, of the nozzle spray disk is thus located within the interior of the mounting nut portion of the nozzle cap, and the opposite, second side, or front surface, of the nozzle spray disk is flush with the end of the mounting nut portion so that there is no rim or cavity between the nozzle and mounting nut as in the '481 patent described above.
The one-piece nozzle cap therefore eliminates the collection of adhesive at the outer surface of the nozzle, and prevents installation of the nozzle upside down, which are potential problems with the nozzle disclosed in the '481 patent. Nevertheless, a number of difficulties are presented in the installation and fabrication of this one-piece nozzle cap. Although formed in one piece, the nozzle cap can be overtightened on the threaded extension of the dispensing device wherein the mounting nut portion is over-torqued causing the nozzle spray disk and boss to deflect or distort against the threaded extension of the spray head. This can create the same type of leakage problems between the through bore in the nozzle and the air jet bores therein described above in connection with the '481 patent.
The above problems are addressed with the construction described in U.S. Pat. No. 5,065,943 issued on Nov. 19, 1991 to B. Boger et al. which is assigned to the same assignee as this invention. In the preferred embodiment, the nozzle cap comprises a mounting piece, or nut, permanently mounted to a nozzle formed with a stepped through bore and a plurality of spaced air jet bores located radially outwardly from the through bore. Both the mounting piece and nozzle are machined separately, and then are substantially permanently interconnected by roll-forming an end of the nut flush with the peripheral edge of the nozzle. When the mounting piece the nozzle cap is assembled on the threaded extension of the adhesive dispensing device, the nozzle is positioned such that its stepped through bore communicates with the adhesive passage in the threaded extension and its air jet bores communicate with the air passageway in the nozzle. An adhesive bead is extruded through the stepped through bore in the nozzle, and this bead is impacted by air jets from the spaced air jet bores which stretch or attenuate the adhesive bead to form an elongated adhesive fiber for deposition in a controlled spiral spray pattern onto a substrate.
One aspect of this invention is therefore predicated on the concept of forming a two-piece nozzle cap in which each piece is separately machined, and then the two pieces are substantially permanently connected to one another. This avoids the installation problems of the type discussed above in connection with the '481 patent, reduces the difficulty and cost of the machining operations and results in less scrap.
With respect to the problem of adhesive leakage described above, the nozzle of the nozzle cap is preferably formed with a seat at the adhesive inlet to its stepped through bore. This seat mounts an O-ring substantially concentric to the stepped through bore, and in a position between the stepped through bore and the air jet bores formed in the nozzle spray disk thereby providing a fluid tight seal between the adhesive and the air jet bores. In addition, the O-ring in combination with a three-stage assembly sequence reduces the potential for overtightening of the nozzle cap during installation.
While the performance and reliability of the above nozzle cap is better than earlier designs, utilization of the interchangeable nozzle requires the manufacture and assembly of a complex nozzle cap comprised of the nozzle and mounting piece. In addition, the nozzle cap mounts on a threaded extension which is an additional component required to mechanically couple the interchangeable nozzle to the two-way valve or distribution plate of the spray head. The mounting piece, or mounting nut, and threaded extension add significant costs to the manufacture and assembly of the spray head. In addition, the threaded extension and mounting nut limit the centerline spacing of the nozzles as will be described.
In most applications, it is desirable to deposit a series or grouping of identical spiral patterns of elongated strands onto a predetermined area of a surface of a substrate. In such applications, the dispensing nozzles are mounted onto threaded extensions which in turn are mounted on the two-way valves or directly on a distribution plate on which the two-way valves are mounted. For example, as described in U.S. Pat. No. 4,815,660 issued on Mar. 28, 1989 to B. Boger, two-way valves which are attached to the manifold surface such that an adhesive passage is provided to each of the two-way valves which controls the flow of adhesive to the nozzle. Nozzles are attached to the two-way valves by a mounting nut which secures the nozzle to a threaded extension extending from an end of each of the two-way valves. The nozzles may be placed in a single row; however, there must be sufficient space between the mounting nuts to permit a wrench or other tool to engage the nut. Therefore, the width of the mounting nut determines the minimum nozzle centerline spacing which, in turn, determines the minimum width of the spiral pattern so that the spiral patterns can maintain the preferred tangential relationship to each other.
In some applications, it is desired that the width of the spiral pattern be less than that permitted by the single row arrangement of the nozzles. Therefore, as described in U.S. Pat. No. 4,983,109, issued on Jan. 8, 1991 to S. Miller, et al., the nozzles may be arranged in two rows with the second row of nozzles having nozzle centerlines located midway between the nozzle centerlines of the first row. That arrangement permits the width of the spiral pattern to be one half of the minimum width available when the nozzles are arranged in a single row.
The two row, staggered nozzle arrangement is implemented with a distribution plate which ports the hot melt adhesive and pressurized air to the two-way valves and from the valves to the threaded extensions mounted on the distribution plate in the two-row staggered pattern. Alternatively, a special adapter plate which has an arrangement of threaded extensions conforming to the desired two row, staggered nozzle pattern is connected to the discharge surface of the distribution plate. The hot melt adhesive passages and air passageways passing through the adapter plate and each of the threaded extensions are in two rows and are in closer proximity than with a single row nozzle arrangement. Therefore, it may not be possible to supply the pressurized air in the preferred orientation with respect to the air passageways in the nozzle.
In typical applications, the substrate on which the adhesive is to be deposited is moving linearly past the two rows of staggered nozzles. Consequently, a selected area on the substrate surface passes beneath each row at a different time. Therefore, in order for the two rows of nozzles to dispense adhesive on the same area, the two-way valves associated with one row of nozzles must be fired at a slightly different time than the two-way valves associated with the second row of nozzles. This timing requirement adds substantial complexity to the valve control mechanism.
Therefore, using a two row, staggered nozzle pattern to accommodate a narrower width of the spiral pattern has the disadvantages of generally requiring an additional expensive adapter plate, and a more complex and expensive two-way valve control mechanism.